This section provides background information related to the present disclosure which is not necessarily prior art.
Composite articles can be formed by using strips of a composite material, such as a fiber-based material like cloth or graphite tape. Typically, a composite or layup is formed on a mandrel or other work surface that conforms to the desired geometry of the finished composite article. The fiber-based substrate material is applied to the mandrel or shaped work surface. The composite may include one or more layers, where each layer can be formed from contacting and/or overlapping strips of the fiber-based substrate material. In such composites, the fiber-based substrate material also comprises a resin. The resin can be cured after the fiber-based substrate material is applied to the work surface and thus can serve to bond single or multiple layers together in the composite.
One of two methods is typically employed for placing resin in impregnated fiber-based substrate material systems: 1) wet winding/layup or 2) pre-impregnating (referred to as “pre-preg”). For wet winding, the dry fiber is “wetted” with the resin as it is used, usually by submersion through a bath. This method is generally less expensive, but is very messy and the “slickness” of the wet fiber poses difficulty in placing the fiber-based substrate material, as well as keeping it in the proper position, on the shaped work surface or mandrel. The second method, pre-impregnating (pre-preg), involves wetting the resin into the fiber-based substrate material in advance, which has conventionally included a step of partially curing the resin so that it has a tacky consistency (e.g., to a B-stage partial cure state), and then winding up the fiber-based substrate material or storing it for later, subsequent use.
The use of pre-preg materials allows for faster placement of the fiber, is cleaner (much less mess during formation and shaping), and the tacky condition greatly improves the ability to keep the fibers in the proper position during placement and handling prior to full curing. Nearly all pre-preg composite materials in use today are based on thermoset resin systems, which cure when subjected to elevated temperatures. Typical cure times range from 30 minutes to 2 hours depending on the cure temperature. However, such cure times could be reduced and the expensive equipment associated with such techniques required for manufacturing could be significantly improved.
While some pre-preg materials employ ultraviolet radiation (UV) cured resins, these UV resin systems do not lend themselves to a partial cure approach (B-stage curing) available with existing thermoset resins. For example, inconsistent tackiness typically results from UV cured resins, thus resulting in an inhomogeneous resin matrix through the fiber-based material. Hence, partially cured UV curable resins have been avoided in pre-preg systems. As such, new methods of forming pre-preg materials would be desirable that could form composite products having superior quality, improve curing times, and reduce equipment expenses.